The present invention relates to an under-hood material for motorcars, prepared by molding a polyamide resin comprising a caproamide component and/or a hexamethylene adipamide component as the major component thereof and having hydrocarbon groups of 6 to 22 carbon atoms as end groups thereof, wherein (a) the number of the hydrocarbon groups is 5 to 100% of the total number of the end groups of the polyamide and (b) a relative viscosity of the polyamide is 2 to 6.
The under-hood material comprising the polyamide resin according to the present invention has a favorable resistance to the anti-freezing agent for pavements mainly composed of a metal halide such as calcium chloride, zinc chloride, etc. and also is excellent in rigidity and heat-resistance.
Recently, a tendency of changing metallic materials into plastic materials has been conspicuous in motorcar industry for the purposes of reducing the weight of motorcars for improving the ratio of the fuel consumption, of preventing rusts and of insulating sounds. Of the plastic materials, since polyamide resins have excellent characteristics such as heat-resistance, oil-resistance, moldability, toughness, etc., its application to the under-hood parts of motorcars including various functional parts, for instance, parts around the engine such as cooling fun, radiator, top and base of a tank, cylinder-head cover, oil pan, timing-belt pulley, etc., gears, valves, piping for brake, fuel tube, parts for fuel system such as fuel strainer, fuel filter, gasoline tank, etc., parts of exhaust gas system such as canister, etc. and parts of electrical system such as wire harness, connector, bands for assembling electric wires, etc. has attracted attentions.
However, since the polyamides relatively used well in general, such as nylon-6 and nylon-66 which have a relatively high concentration of amide groups, substantially have a strong affinity to inorganic metal salts such as calcium chloride, zinc chloride, etc., there is a large defect that the under-hood parts of motorcars made of these polyamides are cracked within a short period of use due to the erosion by a metal salt such as calcium chloride, magnesium chloride, zinc chloride, etc.
Generally, on the roads in cold districts, in winter an anti-freezing agent mainly composed of calcium chloride, magnesium chloride, etc. is sprinkled in a large amount, and in the case where these inorganic metal salts adhere to the under-hood parts of motorcars in an atmosphere at a high temperature, the parts are caused to be cracked and accordingly, there are many dangerous cases of causing motorcar accidents according to the erosion of the under-hood parts.
Therefore, the spread of the use of the under-hood parts made of nylon-6 and nylon-66 for motorcars has been limited because of the insufficient resistance thereof against the anti-freezing agent for pavement in spite of the excellent toughness and heat-resistance, and the low price thereof.
Accordingly at present, for spreading the use of the under-hood parts made of a lower polyamide resin such as nylon-6 and nylon-66 the offer of a material of lower polyamides which has a resistance to metal halides (a resistance to the anti-freezing agent for pavements) equivalent to or higher than that of nylon-11, nylon-12, etc. and is low in price is desired.
As a result of the present inventors' studies, it has been found that a polyamide resin having a relatively high concentration of the amide groups such as nylon-6, nylon-66, etc. and having hydrocarbon groups of 6 to 22 carbon atoms as the end groups thereof in number of larger than 5% of the total number of the end groups is high in the resistance to metal halides and is useful as the material for the under-hood parts of motorcars, and based on this finding, the present invention has been attained.